I soaked the Cylinders of my Volvo Diesel that had been putting out hazy gray Smoke all the time (the Car had sat for 1 Year and after it was running I found I had been driving it with a Thermostat that was opening too soon) and I guessed it was stuck Piston Rings.
Besides changing the Thermostat I changed to one that also had a higher temp and that did not help the Smoke issue.

I was skeptical that the MMO would work but it was cheap. Soaked 1 week and rotated the Engine and soaked again for 3 days. Wanted to soak longer but had to get the Car on the Road.

I did change the Oil before taking it out on the Freeway for some serious driveling. Over the course of 3 Days the gray Smoke cleared up.
So for the Volvo the MMO worked.

I tried the same on the Mercedes to see if it would reduce the Blow-by but I could not see any difference afterwards.

Another Member used the MMO and it raised his compression and reduced the Blow-by but several Months later He had the symptoms He started with. I am guessing His Rings carboned back up; perhaps His Piston Ring Grooves were worn.

When I had that rough idle after the Engine was hot issue after a Valve Adjustment rebuilding the Injectors is what had the biggest effect on reducing that issue.

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84 300D, 82 Volvo 244Gl Diesel